1. Field of the Invention
The present invention relates to a combined battery including a plurality of cells.
2. Description of the Related Art
In recent years, secondary cells have come into wide use even in equipment requiring a high capacity and a high voltage. Such equipment uses a combined battery in which a number of secondary cells are connected in series or in parallel. Examples of the combined battery include those of the monoblock type, which accommodate a plurality of electrode plate groups in one battery container, and those of binding type in which a plurality of cells (secondary cells) are bound by using end plates or binding bands. If there are about 10 electrode plate groups, the monoblock type is effective because of its satisfactory volumetric efficiency. However, in the case of constructing a combined battery by using 10 or more electrode plate groups, cooling efficiency will decrease.
On the other hand, according to the binding type, by forming convex portions such as ribs on a battery container or placing a spacer between battery containers, cooling efficiency can be enhanced. Furthermore, even in the case where one of the cells has a defect, only the defective cell needs to be exchanged. Thus, the binding type is excellent in working efficiency.
However, in the combined battery of the conventional binding type, when the battery container of one cell expands, the surrounding normal cells receive a load generated by the expansion, which may deform the battery container irreversibly. In particular, when convex portions are not formed on side surfaces of the battery container on which an electrode plate group is disposed, the battery container is likely to expand due to the expansion of the electrode plate group, and the battery container may be deformed irreversibly.